This invention relates to improvement in a gas storage canister, for example, using activated carbon or the like in order to treat fuel vapor of an automotive internal combustion engine.
In an automotive internal combustion engine for instance, a gas storage canister is provided to be able to store and release fuel vapor for the purpose of preventing fuel vapor generated in a fuel tank from releasing out of an automotive vehicle. Fuel vapor generated, for example, after a vehicle stopping is temporarily stored in the gas storage canister and is released together with fresh air from the gas storage canister to be introduced into the engine when the engine is operated after the vehicle stopping. Here, the following fact is known: In the gas storage canister using a gas adsorbing material such as activated carbon or the like, an exothermic reaction occurs when fuel vapor is adsorbed to the gas adsorbing material, so that the temperature of the gas adsorbing material rises. This temperature rise lowers a gas adsorbing ability of the gas adsorbing material. In contrast, an endothermic reaction occurs when fuel vapor is desorbed from the gas adsorbing material, so that the temperature of the gas adsorbing material lowers. This temperature drop lowers a gas desorbing ability of the gas adsorbing material.
In order to hold down the temperature variation occurring during such gas adsorption and desorption operations of the canister, mixing a heat accumulative agent with a gas adsorbing material, such as activated carbon has heretofore been discussed. For example, Japanese Patent Provisional Publication No. 2001-248504 discloses a gas storage canister in which the gas adsorbing material is mixed with a heat accumulative agent made of a material having a large specific heat, such as a metal.
However, when a large quantity of heat accumulative agent is blended in the canister, a proportion of the gas adsorbing material necessary for obtaining the inherent gas adsorbing effect relatively lowers, so that a material utilizing a phase changing material as a heat accumulative agent recently attracts the technicians' attention. For example, Japanese Patent Provisional Publication No. 2001-145832 and 2003-311118 disclose a latent heat accumulative type gas adsorbing material formed by sealing in micro-capsules a phase changing material of an aliphatic hydrocarbon, etc. in which the adsorption and discharge of latent heat occur in accordance with the phase change, thereby forming powdered heat accumulative agent including the phase changing material. This powdered heat accumulative agent is mixed with a gas adsorbing material so as to form an integral product, or depositing this powdered heat accumulative agent on a surface of a granular adsorbing material (activated carbon). According to such a heat accumulative agent utilizing latent heat occurring due to the phase change, a temperature variation occurring due to the adsorption and desorption of the fuel vapor is held down by even a comparatively small quantity of heat accumulative agent, and the adsorption and desorption performance of the canister is improved.